A Sampling Valve is a type of valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

 used in process industries that allows taking a representative portion of a fluid

Fluid

In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 (gas

Gas

Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

es, liquid

Liquid

Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

s, fluidized, solid

Solid

Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...

s, or slurries) to test (e.g. by physical measurements, chemical analysis, microbiological examination), typically for the purposes of identification, quality control, or regulatory assessment. It is a valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

 used for sampling

Sampling

Sampling may refer to:*Sampling , converting a continuous signal into a discrete signal*Sampling , converting continuous colors into discrete color components*Sampling , re-using portions of sound recordings in a piece...

.

The Sampling Valve allows the operator to extract a sample of the product from the production line or reactor and safely store it for transportation to the laboratory where it will be analysed or to the archive room where it can be retrieved for further use.

In chemical plant

Chemical plant

A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...

s, a sample can be taken during the process to ensure that the output meets specifications (or that the quality is acceptable), before shipping the chemical good or before accepting the chemical product.

Sampling Problem

When sampling chemical products, it is of utmost importance to select representative material to analyse. The sample must be representative of the lot, and the choice of samples is critical to producing a valid analysis. The statistics of the sampling process are also important.

And in order for a sample to be representative, it must not contain remains of previous batches that might have stay in the valve's "dead space". For example, a ball valve

Ball valve

A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends...

 commonly found in tap valves consists of a ball that control the flow of the liquid. Once the valve is closed, liquid stays in the ball and the next time the valve is opened, that liquid flows first. If a sample is taken using a ball valve

Ball valve

A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends...

, the valve has to be flushed before the sample is taken.

This raises two additional problems:

1. If the liquid is a chemical substance
   Chemical substance
   In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...
   
    that solidifies at room temperature such as polymer
   Polymer
   A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
   
    or other plastics, it can block the valve and prevent a second sample to be taken.
2. The residue of the chemical substance
   Chemical substance
   In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...
   
    that was flushed needs to be recycled or destroyed at a cost both for the chemical plant
   Chemical plant
   A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...
   
    and the environment.

When sampling hazardous chemicals or deadly substances, it is extremely important that the operator is not exposed to toxic fumes or vapours. These can fatally harm people and should they be released in the atmosphere, they will pollute the environment.

Choosing a sample valve

When choosing a Sampling Valve, different factors have to be considered:

• The material, pressure and temperature rating, gaskets, size and position of the valve according to the pipe specification of the plant.
• The handle or actuator type according to the position (reach) of the valve and depending of the chemical to sample (i.e. if the product contains solid particle or not)
• The receptacle to store the sample for transportation (bottles, container, bag, piston injector or syringe)